On 1 Apr 2004 06:19:32 -0800, Darragh wrote:

I'm planning to lay a patio in the summer, laying flagstones on sand
over an existing concreted surface. However, I'm also hoping to put
up 2 raised beds on either side of it (probably using railway sleepers
although I'm only 80% decided on that).

I was thinking I could break up that part of the existing concrete
that will be directly under the beds, and put topsoil on top of that
(I plan to have the beds about 2 foot tall or so). But I was just
wondering if this would provide enough (or too much) drainage?

As long as you put small gaps along the bottom for excess water
to seep out, I think you'll be fine. The only advantage of
breaking up the existing concrete is that then the water can
drain down into the soil below instead of seeping out onto your
new surface.

Also I've heard conflicting stories about railway sleepers
(particularly whether they are too toxic and contaminate soil). Is
there a treatment that ensure they are OK (or should I just line the
inside of the bed with something if I use them?)

I've used sleepers and there were no signs of phytotoxicity or
contamination of the surroundings. Presumably your sleepers, like
mine, are old ones that have been in use for many years. By now
all the volatile components have long since evaporated.

But look out for one thing: when you or a later owner gets tired
of the raised beds, how will you dispose of these sleepers? The
environmental laws here are gradually tightening, and I was very
glad to give away all the sleepers I had, some 10 years ago. I
have a funny idea that had I tried to dispose of them in any
other way, they'd have been called "toxic waste" and I would have
had to pay through the nose to get rid of them.

In the long run, you might be better constructing your raised
beds of brick & mortar.

--
Rodger Whitlock
Victoria, British Columbia, Canada
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